In the prior art, these kinds of thermal expansion valves were used in refrigeration cycles of air conditioners in automobiles and the like. FIG. 7 shows a prior art thermal expansion valve in cross-section together with an explanatory view of the refrigeration cycle. The thermal expansion valve 10 includes a valve housing 30 formed of prismatic-shaped aluminum. The body 30 is associated with a refrigerant duct 11 of the refrigeration cycle having a first path, i.e., passage 32, and a second path, i.e., passage 34. The second passage 34 is placed above the first passage 32 with a distance inbetween. The first passage 32 is for a liquid-phase refrigerant passing through a refrigerant exit of a condenser 5 through a receiver 6 to a refrigerant entrance of an evaporator 8. The second passage 34 is for a liquid-phase refrigerant passing through the refrigerant exit of the evaporator 8 toward a refrigerant entrance of a compressor 4.
An orifice 32a for the adiabatic expansion of the liquid refrigerant supplied from the refrigerant exit of the receiver 6 is formed on the first passage 32, and the first passage 32 is connected to the entrance of the evaporator 8 via the orifice 32a and a passage 321. The orifice 32a has a center line extending along the longitudinal axis of the valve housing 30. A valve seat is formed on the entrance of the orifice 32a. A valve member, such as a ball, 32b supported by a valve member support 32c forms a valve structure together with the valve seat. The valve member 32b and the valve member support 32c are welded and fixed together. The valve member support 32c is fixed onto the valve member 32b and is also forced by a spring 32d, for example, a compression coil spring.
The first passage 32 where the liquid refrigerant from receiver 6 is introduced is a path of the liquid refrigerant, and is equipped with an entrance port 322 and a valve chamber 35 connected thereto. The valve chamber 35 has a floor portion formed on the same axis of the center line of the orifice 32a, and is sealed by a plug 39.
Further, in order to supply drive force to the valve member 32b according to an exit temperature of the evaporator 8, a small hole 37 and a large hole 38 having a greater diameter than the hole 37 is formed on the center line axis extending through the second passage 34. A screw hole 361 for fixing a power element member 36 working as a heat sensor is formed on the upper end of the valve housing 30.
The power element member, i.e., valve controller 36 is comprised of a stainless steel diaphragm 36a, an upper cover 36d and a lower cover 36h each defining an upper pressure activate chamber 36b and a lower pressure activate chamber 36c divided by the diaphragm two sealed chambers are formed above and under the diaphragm 26. A tube 36i is used to encloses a predetermined refrigerant working as a diaphragm driver liquid into the upper pressure activate chamber. The valve controller 36 is fixed to the valve housing 30 by a screw 361. The lower pressure activate chamber 36c is connected to the second passage 34 via a pressure hole 36e extending coaxially with the center line axis of the orifice 32a. A refrigerant vapor from the evaporator 8 flows through the second passage 34. The second passage 34 is a passage for gas phase refrigerant, and the pressure of the refrigerant vapor is applied to the lower pressure activate chamber 36c via the pressure hole 36e.
Further, inside the lower pressure activate chamber 36c is a heat sensing shaft 36f and an activating shaft 37f made of stainless steel. The heat sensing shaft 36f is exposed vertically inside the second passage 34 is slidably positioned through the second passage 34 inside the large hole 38. The shaft 36f contacts the diaphragm 36a transmit to the refrigerant exit temperature of the evaporator 8 to the lower pressure activate chamber 36c. This provides a driving force, in response to the displacement of the diaphragm 36a according to the pressure difference between the upper pressure activate chamber 36b and the lower pressure activate chamber 36c, by moving the shaft 36f inside the large hole 38. The activating shaft 37f is slidably positioned inside the small hole 37 and applies pressure to the valve member 32b against the spring force of the spring 32d according to the displacement of the heat sensing shaft 36f. The heat sensing shaft 36f comprises a stopper portion 312 having a large diameter, which portion 312 works as a receive member of the diaphragm 36a. The diaphragm 36a is positioned to contact its surface, a large diameter portion 314 contacts the lower surface of the stopper portion 312 at one end surface and is slideably movable inside the lower pressure activate chamber 36c. A heat sensing portion 318 contacts the other end surface of the large diameter portion 314 at an upper end surface of the shaft 36f. The other end surface of the shaft 36f is connected to the activating shaft 37f.
Further, the heat sensing shaft 36f is equipped with an annular sealing member, for example, an o-ring 36g, for securing the seal of the first passage 32 and the second passage 34. The heat sensing shaft 36f and the activating shaft 37f are positioned so as to contact each other. The activating shaft 37f also contacts the valve member 32b. The heat sensing shaft 36f and the activating shaft 37f together form a valve driving shaft or rod member.
In the above explained structure of a thermal expansion valve, a known diaphragm driving liquid is filled inside the upper pressure activating chamber 36b placed above an upper cover 36d. The heat of the refrigerant vapor from the refrigerant exit of the evaporator 8 the flows through the second passage 34 and to the diaphragm 36a via the shaft 36f. The valve driving shaft transmits heat to the diaphragm driving liquid.
The diaphragm driving liquid inside the upper pressure activate chamber 36b adds pressure to the upper surface of the diaphragm 36a by turning into gas in correspondence to the heat transmitted thereto. The diaphragm 36a is displaced in the upper and lower direction according to the difference between the pressure of the diaphragm driving gas added to the upper surface thereto and the pressure added to the lower surface thereto.
The displacement of the center portion of the diaphragm 36a to the upper and lower direction is transmitted to the valve member 32b via the valve member driving shaft and moves the valve member 32b close to or away from the valve seat of the orifice 32a. As a result, the refrigerant flow rate is controlled.
That is, the gas phase refrigerant temperature of the exit side of the evaporator 8 is transmitted to the upper pressure activate chamber 36b, and according to the temperature, the pressure inside the upper pressure activate chamber 36b changes, and the exit temperature of the evaporator 8 rises. When the heat load of the evaporator rises, the pressure inside the upper pressure activate chamber 36b rises, and accordingly, the heat sensing shaft 36f or valve member driving shaft is moved to the downward direction and pushes down the valve member 32b via the activating shaft 37, resulting in a wider opening of the orifice 32a. This increases the supply rate of the refrigerant to the evaporator, and lowers the temperature of the evaporator 8. In reverse, when the exit temperature of the evaporator 8 decreases and the heat load of the evaporator decreases, the valve member 32b is driven in the opposite direction, resulting in a smaller opening of the orifice 32a. As the supply rate of the refrigerant to the evaporator decreases, the temperature of the evaporator 8 rises.
In the thermal expansion valve explained above, an o-ring 40 is utilized as a sealing member, and the enlarged cross-sectional view of the o-ring 40 is shown in FIG. 8. In the drawing, o-ring 40 is formed by molding a rubber material, such as silicon rubber, into a ring shape, and the cross-sectional surface 410 has a round shape.
The mold used to form the o-ring is comprised of an upper mold and a lower mold each corresponding to the upper and lower half of the o-ring. Therefore, seams 420 and 422 corresponding to the matching portion of the upper and lower molds will be formed on the outer and inner peripheral of the ring.
When inserting the o-ring to the large hole 38 of the thermal expansion valve 10 in the arrow F direction, the outer seam 420 will be rubbed against the wall surface 38a of the hole 38, and a torsion stress shown by arrows R.sub.1 and R.sub.2 is added to the o-ring 40, resulting in a torsion of the o-ring. When such torsion occurs in the o-ring, the effect as a seal member will decrease, causing problems such as leakage.
Further, the seams 420 and 422 of the o-ring exist in the sealing portion, so it may cause leakage and other problems.
Even further, the rubbing resistance when utilizing the o-ring 40 as the seal member is too large.
Therefore, the object of the present invention is to provide a thermal expansion valve with the above problems solved.